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a
Microprocessor
Supervisory Circuits
ADM691A/ADM693A/ADM800L/M
FEATURES
Low Power Consumption:
Precision Voltage Monitor
62% Tolerance on ADM800L/M
Reset Time Delay—200 ms, or Adjustable
1 mA Standby Current
Automatic Battery Backup Power Switching
Fast Onboard Gating of Chip Enable Signals
Also Available in TSSOP Package (ADM691A)
APPLICATIONS
Microprocessor Systems
Computers
Controllers
Intelligent Instruments
Automotive Systems
Critical mP Power Monitoring
FUNCTIONAL BLOCK DIAGRAM
BATT ON
4.65V1
VCC
VOUT
VBATT
CHIP ENABLE
OUTPUT
CONTROL
The ADM691A/ADM693A/ADM800L/ADM800M family of
supervisory circuits offers complete single chip solutions for
power supply monitoring and battery control functions in
microprocessor systems. These functions include µP reset,
backup-battery switchover, watchdog timer, CMOS RAM write
protection, and power-failure warning. The family of products
provides an upgrade for the MAX691A/93A/800M family of
products.
CEOUT
CEIN
OSC IN
OSC SEL
RESET &
WATCHDOG
TIMEBASE
RESET &
GENERATOR
RESET
RESET
WATCHDOG
INPUT (WDI)
GENERAL DESCRIPTION
LOW LINE
WATCHDOG
TRANSITION DETECTOR
WATCHDOG
OUTPUT (WDO)
WATCHDOG
TIMER
POWER FAIL
INPUT (PFI)
POWER FAIL
OUTPUT (PFO)
1.25V
ADM691A/ADM693A
ADM800L/ADM800M
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All parts are available in 16-pin DIP and SO packages. The
ADM691A is also available in a space-saving TSSOP package.
The following functionality is provided:
1. Power-on reset output during power-up, power-down and
brownout conditions. The circuitry remains operational with
VCC as low as 1 V.
2. Battery backup switching for CMOS RAM, CMOS microprocessor or other low power logic.
3. A reset pulse if the optional watchdog timer has not been
toggled within a specified time.
4. A 1.25 V threshold detector for power fail warning, low battery detection, or to monitor a power supply other than +5 V.
1VOLTAGE
INPUT
POWER
DETECTOR = 4.4V (ADM693A/ADM800M)
+5V
7805
0.1µF
VCC
CMOS
RAM
R1
VCC
VBATT
BATTERY
PFI
GND
R2
NC
BAT
ON
VOUT
CEOUT
ADM691A CEIN
ADM693A
ADM800L
ADM800M WDI
PFO
OSC IN
OSC SEL
LOW LINE
ADDRESS
DECODE
RESET
A0–A15 µP
POWER
I/O LINE
NMI
µP
RESET
WDO
SYSTEM
STATUS
INDICATORS
Figure 1. Typical Application
REV. 0
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
World Wide Web Site: http://www.analog.com
Fax: 617/326-8703
© Analog Devices, Inc., 1996
ADM691A/ADM693A/ADM800L/M–SPECIFICATIONS
(VCC = 4.75 V to 5.5 V (ADM691A, ADM800L) 4.5 V to 5.5 V (ADM693A, ADM800M) VBATT = +2.8 V, TA = TMIN to TMAX unless otherwise noted)
Parameter
Min
BATTERY BACKUP SWITCHING
VCC, VBATT Operating Voltage Range
VOUT Output Voltage
VCC to VOUT Output Resistance
VOUT in Battery Backup Mode
0
VCC – 0.05
VCC – 0.3
Typ
5.5
V
V
V
Ω
V
V
V
Ω
Ω
Ω
µA
µA
1.2
70
0.04
12
20
25
100
1
VBATT – 0.3
VBATT – 0.25
VBATT – 0.15
–0.1
–1.0
Battery Switchover Threshold
VCC–VBATT
Battery Switchover Hysteresis
BATT ON Output Voltage Low
BATT ON Output Short Circuit Current
1
RESET AND WATCHDOG TIMER
Reset Voltage Threshold
ADM691A, ADM800L
ADM693A, ADM800M
ADM800L, VCC Falling
ADM800M, VCC Falling
Reset Threshold Hysteresis
VCC to RESET Delay
LOW LINE to RESET Delay
Reset Timeout Period Internal Oscillator
Reset Timeout Period External Clock
Watchdog Timeout Period, Internal Oscillator
Unit
VCC – 0.02
VCC – 0.2
0.8
VBATT to VOUT Output Resistance
Supply Current (Excludes IOUT)
Supply Current in B. Backup (Excludes IOUT)
Battery Standby Current
(+ = Discharge, – = Charge)
Max
4.5
4.25
4.55
4.3
+0.02
+0.02
VBATT + 0.03
VBATT – 0.03
60
0.1
0.4
0.7
1.5
60
15
100
4.65
4.40
4.75
4.50
4.70
4.45
µA
µA
V
V
mV
V
V
mA
µA
V
V
V
V
mV
µs
ns
ms
Cycles
s
ms
Cycles
Cycles
ns
V
V
V
mA
V
V
V
µA
V
V
mA
Test Conditions/Comments
IOUT = 25 mA
IOUT = 250 mA
VCC = 4.5 V
VBATT = 4.5 V, IOUT = 20 mA
VBATT = 2.8 V, IOUT = 10 mA
VBATT = 2.0 V, IOUT = 5 mA
VBATT = 4.5 V
VBATT = 2.8 V
VBATT = 2.0 V
VCC > (VBATT – 1 V)
VCC < (VBATT – 1.2 V), VBATT = 2.8 V
5.5 V > VCC > VBATT + 0.2 V
(VBATT +0.2 V) < VCC , TA = +25°C
(VBATT +0.2 V) < VCC
Power Up
Power Down
ISINK = 3.2 mA
ISINK = 25 mA
Sink Current
Source Current
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140
1.0
70
Watchdog Timeout Period, External Clock
Minimum WDI Input Pulse Width
RESET Output Voltage
15
80
800
200
2048
1.6
100
4096
1024
280
2.25
140
100
0.004
0.1
0.3
0.4
7
0.4
20
3.5
RESET Output Short Circuit Current
RESET Output Voltage Low
LOW LINE Output Voltage
LOW LINE Short Circuit Source Current
WDO Output Voltage
0.1
0.4
3.5
1
15
100
0.4
3.5
WDO Short Circuit Source Current
WDI Input Threshold
Logic Low
Logic High
WDI Input Current
POWER FAIL DETECTOR
PFI Input Threshold ADM69xA
PFI Input Threshold ADM800L/M
PFI Input Current
PFO Output Voltage
PFO Short Circuit Source Current
PFI to PFO Delay
3
0.75 × VCC
–50
1.2
1.225
3.5
1
10
0.8
–10
20
1.25
1.25
± 0.01
15
25
60
–2–
50
V
V
µA
µA
1.3
1.275
± 25
0.4
V
V
nA
V
100
µA
µs
µs
TA = +25°C
TA = +25°C
Power Down
Power Up
Power Up
Long Period
Short Period
Long Period
Short Period
VIL = 0.4, VIH = 0.75 × VCC
ISINK = 50 µA, VCC = 1 V, VBATT = 0 V
ISINK = 3.2 mA, VCC = 4.25 V
ISOURCE = 1.6 mA, VCC = 5 V
ISINK = 3.2 mA
ISINK = 3.2 mA, VCC = 4.25 V
ISOURCE = 1 µA, VCC = 5 V
ISINK = 3.2 mA, VCC = 4.25 V
ISOURCE = 500 µA, VCC = 5 V
WDI = 0 V
WDI = VOUT
VCC = 5 V
VCC = 5 V
ISINK = 3.2 mA
ISOURCE = 1 µA
VIN = –20 mV
VIN = 20 mV
REV. 0
ADM691A/ADM693A/ADM800L/M
Parameter
Min
CHIP ENABLE GATING
CEIN Leakage Current
CEIN to CEOUT Resistance
CEIN to CEOUT Propagation Delay
CEOUT Short-Circuit Current
CEOUT Output Voltage
0.1
3.5
2.7
RESET to CEOUT Propagation Delay
OSCILLATOR
OSC IN Input Current
OSC In Input Pullup Current
OSC SEL Input Pullup Current
OSC IN Frequency Range
OSC IN Threshold Voltage
Typ
Max
Units
Test Conditions/Comments
± 0.005
40
6
0.75
±1
150
10
2.0
µA
Ω
ns
mA
V
V
µs
Disable Mode
Enable Mode
RIN = 50 Ω, CLOAD = 50 pF
Disable Mode, CEOUT = 0 V
VCC = 5 V, IOUT = –100 µA
VCC = 0 V, VBATT = 2.8 V, IOUT = 1 µA
Power Down
±5
100
100
µA
µA
µA
kHz
V
V
kHz
OSC SEL = 0 V
OSC SEL = VOUT or Floating
OSC SEL = 0 V
OSC SEL = 0 V
VIH
VIL
OSC SEL = 0 V, COSC = 47 pF
12
0.1
10
10
500
VOUT – 0.6
3.65
100
VOUT – 0.4
OSC IN Frequency with Ext Capacitor
2.00
NOTES
1
Either V CC or VBATT can be 0 V if the other > +2.0 V.
Specifications subject to change without notice.
ABSOLUTE MAXIMUM RATINGS*
ORDERING GUIDE
(TA = 25°C unless otherwise noted)
VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +6 V
VBATT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +6 V
All Other Inputs . . . . . . . . . . . . . . . . . –0.3 V to VOUT + 0.5 V
Input Current
VCC (Peak) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1000 mA
VCC (Continuous) . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 mA
VBATT (Peak) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 mA
VBATT (Continuous) . . . . . . . . . . . . . . . . . . . . . . . . . . 25 mA
GND, BATT ON . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 mA
Digital Output Current . . . . . . . . . . . . . . . . . . . . . . . . . 25 mA
Power Dissipation, N-16 DIP . . . . . . . . . . . . . . . . . . 842 mW
θϑA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 135°C/W
Power Dissipation, R-16 Narrow SOIC . . . . . . . . . . . 700 mW
θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . . . 110°W
Power Dissipation, R-16 Wide SOIC . . . . . . . . . . . . . 762 mW
θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 110°C/W
Power Dissipation, RU-16 TSSOP . . . . . . . . . . . . . . 500 mW
θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 158°C/W
Operating Temperature Range
Industrial (A Version) . . . . . . . . . . . . . . . . –40°C to +85°C
Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . +300°C
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . . 215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . +220°C
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
Model
Temperature
Range
Package
Option
ADM691AAN
ADM691AARN
ADM691AARW
ADM691AARU
ADM693AAN
ADM693AARN
ADM693AARW
ADM800LAN
ADM800LARN
ADM800LARW
ADM800MAN
ADM800MARN
ADM800MARW
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
N-16
R-16N
R-16W
RU-16
N-16
R-16N
R-16W
N-16
R-16N
R-16W
N-16
R-16N
R-16W
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*Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and functional operation of
the device at these or any other conditions above those listed in the operational
sections of this specification is not implied. Exposure to absolute maximum ratings
for extended periods of time may affect device reliability.
Table I. Product Selection Table
Part No.
Power On
Reset Time
Low VCC
Threshold
Watchdog
Timeout
Battery Backup
Switching
Base Drive
Ext PNP
Chip Enable
Signals
ADM691A
ADM693A
ADM800M
ADM800L
200 ms or Adj.
200 ms or Adj.
200 ms or Adj.
200 ms or Adj.
4.65 V ± 3%
4.4 V ± 3%
4.4 V ± 2%
4.65 V ± 2%
100 ms, 1.6 s, Adj.
100 ms, 1.6 s, Adj.
100 ms, 1.6 s, Adj.
100 ms, 1.6 s, Adj.
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
REV. 0
–3–
ADM691A/ADM693A/ADM800L/M
PIN DESCRIPTIONS
Pin
Mnemonic
Function
1
VBATT
2
VOUT
3
4
5
VCC
GND
BATT ON
6
LOW LINE
7
OSC IN
8
OSC SEL
9
PFI
10
PFO
11
WDI
12
CEOUT
13
14
CEIN
WDO
15
RESET
16
RESET
Backup Battery Input. Connect to external battery or capacitor. Connect to ground if a backup battery is
not used.
Output Voltage, VCC or VBATT is internally switched to VOUT depending on which is at the highest potential. When VCC is higher than VBATT and is also higher than the reset threshold, VCC is switched to VOUT.
When VCC is lower than VBATT and below the reset threshold, VBATT is switched to VOUT. Connect VOUT to
VCC if a backup battery is not being used.
Power Supply Input; +5 V.
0 V. Ground reference for all signals.
Logic Output. BATT ON goes high when VOUT is internally switched to the VBATT input. It goes low when
VOUT is internally switched to VCC. The output may also be used to drive the base (via a resistor) of an external PNP transistor to increase the output current above the 250 mA rating of VOUT.
Logic Output. LOW LINE goes low when VCC falls below the reset threshold. It returns high as soon as
VCC rises above the reset threshold.
Oscillator Logic Input. With OSC SEL high or floating, the internal oscillator is enabled and sets the reset
delay and the watchdog timeout period. Connecting OSC IN low selects 100 ms while leaving it floating
selects 1.6 sec. With OSC SEL low, OSC IN can be driven by an external clock signal or an external capacitor can be connected between OSC IN and GND. This sets both the reset active pulse timing and the
watchdog timeout period. (See Table II and Figure 4.)
Logic Oscillator Select Input. When OSC SEL is unconnected (floating) or driven high, the internal oscillator sets the reset active time and watchdog timeout period. When OSC SEL is low, the external oscillator
input, OSC IN, is enabled. OSC SEL has a 10 µA internal pullup.
Power Fail Input. PFI is the noninverting input to the Power Fail Comparator. When PFI is less than
1.25 V, PFO goes low. Connect PFI to GND or VOUT when not used.
Power Fail Output. PFO is the output of the Power Fail Comparator. It goes low when PFI is less than
1.25 V.
Watchdog Input. WDI is a three level input. If WDI remains either high or low for longer than the watchdog timeout period, RESET pulses low and WDO goes low. The timer resets with each transition on the
WDI line. The Watchdog Timer may be disabled if WDI is left floating or is driven to midsupply.
Output. CEOUT goes low only when CEIN is low and VCC is above the reset threshold. If CEIN is low when
reset is asserted, CEOUT will remain low for 15 µs or until CEIN goes high, whichever occurs first.
Chip Enable Input. The input to the CE gating circuit. Connect to GND or VOUT if not used.
Logic Output. The Watchdog Output, WDO, goes low if WDI remains either high or low for longer than
the Watchdog timeout period. WDO is set high by the next transition at WDI. WDO remains high if WDI
is unconnected.
Logic Output. RESET goes low if VCC falls below the Reset Threshold. It remains low for 200 ms typ after
VCC goes above the reset threshold.
Logic Output. RESET is an open-drain output. It is the inverse of RESET.
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PIN CONFIGURATIONS
VBATT
1
16 RESET
VOUT
2
15 RESET
VCC
3
GND
4
BATT ON
5
LOW LINE
6
OSC IN
OSC SEL
ADM691A
ADM693A
ADM800L
ADM800M
14 WDO
13
CEIN
12 CEOUT
11 WDI
TOP VIEW
7 (Not to Scale) 10 PFO
8
9
–4–
PFI
REV. 0
Typical Performance Curves– ADM691A/ADM693A/ADM800L/M
1.2
100
VCC TO VOUT ON RESISTANCE – R
VCC SUPPLY CURRENT – µA
90
80
70
60
50
40
1.1
1.0
0.9
0.8
0.7
30
20
–50
–25
0
25
50
75
TEMPERATURE – °C
100
0.6
–50
125
–30
–10
10
30
50
TEMPERATURE – °C
70
90
Figure 5. VCC to VOUT ON-Resistance vs. Temperature
Figure 2. ICC vs. Temperature: Normal Operation
80
60
60
VCC TO VOUT – mV
BATTERY SUPPLY CURRENT – nA
70
55
50
45
40
ROUT = 0.67Ω
50
40
30
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20
35
10
30
–50
–30
–10
10
30
50
TEMPERATURE – °C
70
0
40
90
60
80
IOUT – mA
100
120
Figure 6. VCC to VOUT Voltage Drop vs. Current
Figure 3. IBATT vs. Temperature: Battery Backup Mode
70
80
60
ROUT = 7Ω
VBATT TO VOUT – mV
CEON RESISTANCE – Ω
70
60
50
40
30
20
–50
40
30
20
10
0
–25
0
25
50
75
TEMPERATURE – °C
100
4
125
6
8
10
IOUT – mA
Figure 7. VBATT to VOUT Voltage Drop vs. Current
Figure 4. Chip Enable ON-Resistance vs. Temperature
REV. 0
50
–5–
ADM691A/ADM693A/ADM800L/M
16
10
VBATT = 2.8V
9
14
PROPAGATION DELAY – ns
8
IBATT – µA
7
6
5
4
3
2
0.5
1.0
1.5
2.0
2.5
3.0
VCC – V
3.5
4.0
4.5
5.0
6
4
0
50
100
150
200
250
300
LOAD CAPACITANCE – pF
Figure 11. Chip Enable Propagation Delay vs.
Load Capacitance
100
230
220
LONG WATCHDOG TIMEOUT PERIOD
RESET DELAY – ms
WATCHDOG AND RESET TIMEOUT PERIOD – s
8
0
0
Figure 8. Battery Current vs. Input Supply Voltage
10
RESET ACTIVE
TIMEOUT PERIOD = >
1
210
200
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SHORT WATCHDOG
TIMEOUT PERIOD
190
180
0.1
10
100
COSC – pF
170
–50
1k
1200
6.5
1000
RESET OUTPUT RESISTANCE – Ω
7.0
6.0
5.5
5.0
4.5
4.0
–50
–25
0
25
50
75
TEMPERATURE – °C
100
–30
–10
10
30
50
TEMPERATURE – °C
70
90
Figure 12. Reset Timeout Relay vs. Temperature
Figure 9. Watchdog and Reset Timeout Period vs.
OSC IN Capacitor
PROPAGATION DELAY – ns
10
2
1
0
12
600
400
Figure 10. Chip Enable Propagation Delay vs.
Temperature
VCC = 0V, VBATT = 2.8V
SINKING CURRENT
200
0
–50
125
VCC = 5V, VBATT = 2.8V
SOURCING CURRENT
800
–20
40
70
10
TEMPERATURE – °C
100
130
Figure 13. RESET Output Resistance vs. Temperature
–6–
REV. 0
ADM691A/ADM693A/ADM800L/M
100
100
90
90
10
10
0%
0%
1V
400ms
1V
Figure 14. RESET Output Voltage vs. Supply
POWER FAIL RESET OUTPUT
RESET is an active low output that provides a reset signal to the
Microprocessor whenever VCC is at an invalid level. When VCC
falls below the reset threshold, the RESET output is forced
low. The reset voltage threshold is 4.65 V (ADM691A/
ADM800L) or 4.4 V (ADM693A/ADM800M).
On power-up RESET will remain low for 200 milliseconds after
VCC rises above the appropriate reset threshold. This allows time
for the power supply and microprocessor to stabilize. On powerdown, the RESET output remains low with VCC as low as 1 V.
This ensures that the microprocessor is held in a stable shutdown condition. If RESET is required to be low for voltages below 1 V, this may be achieved by connecting a pull-down resistor
on the RESET line. The resistor will help maintain RESET low
down to VCC = 0 V. Note that this is only necessary if VBATT is
below 2 V. With battery voltages ≥2 V RESET will function correctly with VCC from 0 V to +5.5 V.
10µs
Figure 15. RESET Response Time
The normal (short) timeout period becomes effective following
the first transition of WDI after reset has gone inactive. The
watchdog timeout period restarts with each transition on the
WDI pin. To ensure that the watchdog timer does not time out,
either a high-to-low or low-to high transition on the WDI pin
must occur at or less than the minimum timeout period. If WDI
remains permanently either high or low, reset pulses will be issued after each timeout period (1.6 seconds). The watchdog
monitor can be deactivated by floating the Watchdog Input
(WDI). If floating, an internal resistor network biases WDI to
around 1.6 V.
BATT ON
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4.65V1
VCC
VOUT
This reset active time is adjustable by using an external oscillator
or by connecting an external capacitor to the OSC IN pin. Refer
to Table II.
VBATT
CHIP ENABLE
OUTPUT
CONTROL
The guaranteed minimum and maximum thresholds of the
ADM691A/ADM800L are 4.5 V and 4.75 V, while the guaranteed thresholds of the ADM693A/ADM800M are 4.25 V and
4.5 V. The ADM691A/ADM800L is therefore compatible with
5 V supplies with a +10%, –5% tolerance while the ADM693A/
ADM800M is compatible with 5 V ± 10% supplies.
CEOUT
CEIN
OSC IN
OSC SEL
RESET &
WATCHDOG
TIMEBASE
WATCHDOG
TRANSITION DETECTOR
REV. 0
WATCHDOG
TIMER
POWER FAIL
INPUT (PFI)
RESET
WATCHDOG
OUTPUT (WDO)
POWER FAIL
OUTPUT (PFO)
1.25V
ADM691A/ADM693A
ADM800L/ADM800M
Watchdog Timer Reset
The watchdog timer is restarted at the end of reset, whether the
reset was caused by lack of activity on WDI or by VCC falling below the reset threshold.
RESET &
GENERATOR
RESET
WATCHDOG
INPUT (WDI)
In addition to RESET an active high RESET output is provided.
This is the complement of RESET and is useful for processors
requiring an active high RESET signal.
The watchdog timer circuit monitors the activity of the microprocessor in order to check that it is not stalled in an indefinite
loop. An output line on the processor is used to toggle the
Watchdog Input (WDI) line. If this line is not toggled within the
selected timeout period, a reset pulse is generated. The watchdog timeout period may be configured for either a fixed “short”
100 ms or a “long” 1.6 second timeout period or for an adjustable timeout period. Note that even if the short timeout period
is selected, the first time out immediately following a reset is
1.6 sec. This is to allow additional time for the microprocessor
to regain control following a reset.
LOW LINE
1VOLTAGE
DETECTOR = 4.4V (ADM693A/ADM800M)
Figure 16. Functional Block Diagram
Watchdog Output (WDO)
The Watchdog Output WDO provides a status output that goes
low if the watchdog timer “times out” and remains low until set
high by the next transition on the watchdog input. WDO is also
set high when VCC goes below the reset threshold. If WDI remains high or low indefinitely, RESET and RESET will generate 200 ms pulses every 1.6 sec.
–7–
ADM691A/ADM693A/ADM800L/M
When VCC is below the reset threshold, the watchdog function is
disabled and WDI goes high impedance as it is disconnected
from its internal resistor network.
Changing the Watchdog and Reset Timeout
The watchdog and reset timeout periods may be controlled using OSC SEL and OSC IN. Please refer to Table II. With both
these inputs floating (or connected to VOUT) as in Figure 16, the
reset timeout is fixed at 200 ms and the watchdog timeout is
fixed at 1.6 sec.. If OSC IN is connected to GND as in Figure
16, the reset timeout period remains at 200 ms but a short
(100 ms) watchdog timeout period is selected (except immediately following a reset where it reverts to 1.6 sec). By connecting
OSC SEL to GND it is possible to select alternative timeout periods by either connecting a capacitor from OSC IN to GND or
by overdriving OSC IN with an external clock. With an external
capacitor, the watchdog timeout period is
The internal oscillator is enabled when OSC SEL is high or
floating. In this mode, OSC IN selects between the 1.6 second
and 100 ms watchdog timeout periods.
VCC
OSC SEL
tRS
RESET
THRESHOLD
tRS
80µs
80µs
RESET
Twd (ms) = 600 (C/47 pF)
RESET
and the reset active period is
Treset (ms) = 1200 (C/47 pF)
CEIN
With an external clock connected to OSC IN, the timeout
periods become
12µs
CEOUT
Twd = 1024 (1/fCLK)
Treset = 2048 (1/fCLK)
Figure 17. RESET and Chip Enable Timing
Battery-Switchover Section
During normal operation with VCC higher than the reset threshold and higher than VBATT, VCC is internally switched to VOUT
via an internal PMOS transistor switch. This switch has a typical on-resistance of 0.75 Ω and can supply up to 250 mA at the
VOUT terminal. VOUT is normally used to drive a RAM memory
bank which may require instantaneous currents of greater than
250 mA. If this is the case then a bypass capacitor should be
connected to VOUT. The capacitor will provide the peak current
transients to the RAM. A capacitance value of 0.1 µF or greater
may be used.
8
OSC SEL
ADM69_A
ADM800_
7
CLOCK
0 TO 250kHz
www.BDTIC.com/ADI
OSC IN
Figure 18a. External Clock Source
If the continuous output current requirement at VOUT exceeds
250 mA or if a lower VCC–VOUT voltage differential is desired,
an external PNP pass transistor may be connected in parallel
with the internal transistor. The BATT ON output can drive
the base of the external transistor.
NC
8
OSC SEL
ADM69_A
ADM800_
NC
If VCC drops below VBATT and below the reset threshold, battery
backup is selected. A 7 Ω MOSFET switch connects the VBATT
input to VOUT. This MOSFET has very low input-to-output
differential (dropout voltage) at the low current levels required for
battery backup of CMOS RAM or other low power CMOS circuitry. The supply current in battery backup is typically 0.04 µA.
7
OSC IN
Figure 18b. Internal Oscillator (1.6 s Watchdog)
8
OSC SEL
ADM69_A
ADM800_
7
High value capacitors, either standard electrolytic or the faradsize double layer capacitors, can also be used for short-term
memory backup.
OSC IN
COSC
If the battery-switchover section is not used, VBATT should be
connected to GND and VOUT should be connected to VCC.
Figure 18c. External Capacitor
Table II. Reset Pulse Width and Watchdog Timeout Selections
OSC SEL
OSC IN
Watchdog Timeout Period
Normal
Immediately After Reset
Reset Active Period
Low
Low
Floating
Floating
External Clock Input
External Capacitor
Low
Floating or VOUT
1024 clks
600 ms × C/47 pF
100 ms
1.6 s
2048 clks
1200 ms × C/47 pF
200 ms
200 ms
–8–
4096 clks
2.4 s × C/47 pF
1.6 s
1.6 s
REV. 0
ADM691A/ADM693A/ADM800L/M
8
INPUT
POWER
OSC SEL
R1
ADM69_A
ADM800_
7
OSC IN
POWER
FAIL
INPUT
1.25V
PFO
POWER
FAIL
OUTPUT
R2
COSC
Figure 20. Power Fail Comparator
Figure 18d. Internal Oscillator (100 ms Watchdog)
Table III. Input and Output Status in Battery Backup Mode
WDI
Signal
Status
VBATT
VOUT
Supply Current is <1 µA.
VOUT is connected to VBATT via an internal
PMOS switch.
Switchover comparator monitors VCC for
active switchover.
0 V.
Logic High. The open circuit voltage is equal
to VOUT.
Logic Low.
OSC IN is ignored.
OSC SEL is ignored.
The Power Fail Comparator remains active in
the battery-backup mode for VCC ≥ VBATT
–1.2 V. With VCC lower than this, PFO is
forced low.
The Power Fail Comparator remains active in
the battery-backup mode for VCC ≥ VBATT
–1.2 V. With VCC lower than this, PFO is
forced low.
WDI is ignored.
Logic High. The open circuit voltage is equal
to VOUT.
High Impedance.
Logic High. The open circuit voltage is equal
to VOUT.
Logic Low.
High Impedance.
WDO
VCC
t2
t3
GND
BATT ON
RESET
t1
t1
t1
t1 = RESET TIME.
t2 = NORMAL (SHORT) WATCHDOG TIMEOUT PERIOD.
LOW LINE
OSC IN
OSC SEL
PFI
t3 = WATCHDOG TIMEOUT PERIOD IMMEDIATELY FOLLOWING A RESET.
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Figure 19. Watchdog Timing
CE Gating and RAM Write Protection
PFO
All products include memory protection circuitry which ensures
the integrity of data in memory by preventing write operations
when VCC is at an invalid level. There are two additional pins,
CEIN and CEOUT, that control the Chip Enable or Write inputs
of CMOS RAM. When VCC is present, CEOUT is a buffered replica of CEIN, with a 5 ns propagation delay. When VCC falls below the reset voltage threshold, an internal gate forces CEOUT
high, independent of CEIN.
WDI
CEOUT
CEOUT typically drives the CE, CS, or Write input of battery
backed up CMOS RAM. This ensures the integrity of the data
in memory by preventing write operations when VCC is at an invalid level. Similar protection of EEPROMs can be achieved by
using the CEOUT to drive the Store or Write inputs of an
EEPROM, EAROM, or NOVRAM.
RESET
RESET
CEIN
WDO
Power Fail Warning Comparator
An additional comparator is provided for early warning of failure in the microprocessor’s power supply. The Power Fail Input
(PFI) is compared to an internal +1.25 V reference. The Power
Fail Output (PFO) goes low when the voltage at PFI is less than
1.3 V. Typically PFI is driven by an external voltage divider that
senses either the unregulated dc input to the system’s 5 V regulator or the regulated 5 V output. The voltage divider ratio can
be chosen such that the voltage at PFI falls below 1.25 V several
milliseconds before the +5 V power supply falls below the reset
threshold. PFO is normally used to interrupt the microprocessor
so that data can be stored in RAM and the shut- down procedure executed before power is lost.
REV. 0
–9–
ADM691A/ADM693A/ADM800L/M
INPUT
POWER
APPLICATIONS INFORMATION
INCREASING THE DRIVE CURRENT
R1
If the continuous output current requirements at VOUT exceeds
250 mA or if a lower VCC–VOUT voltage differential is desired, an
external PNP pass transistor may be connected in parallel with
the internal transistor. The BATT ON output can drive the
base of the external transistor via a current limiting transistor.
(PFO)
1.25V
PFI
R2
R3
VH = 1.25 1+
PNP
TRANSISTOR
+5V
INPUT
POWER
0.1µF
5V
0.1µF
VL = 1.25+R1
VBATT
VOUT
BATT
ON
R2+R3
R2 × R3
R1
1.25 VCC–1.25
R2
R3
VMID= 1.25
PFO
VCC
TO
µP NMI
R1+R2
R2
0V
BATTERY
0V
VM
VL
VIN
Figure 23. Adding Hysteresis to the Power Fail Comparator
Figure 21. Increasing the Drive Current
Using a Rechargeable Battery for Backup
Typical Operating Circuit
If a capacitor or a rechargeable battery is used for backup, then
the charging resistor should be connected to VOUT since this
eliminates the discharge path that would exist during power
down if the resistor were connected to VCC.
A typical operating circuit is shown in Figure 24. The circuit
features power supply monitoring, battery backup switching
and watchdog timing.
+5V
INPUT
POWER
I=
CMOS RAM is powered from VOUT . When 5 V power is
present, this is routed to VOUT. If VCC fails, then VBATT is
routed to VOUT. VOUT can supply up to 250 mA from VCC, but
if more current is required, an external PNP transistor can be
added. When VCC is higher than VBATT and the reset threshold,
BATT ON goes low, providing base drive for the external transistor. When VCC is lower than VBATT and the reset threshold,
an internal 7 Ω. MOSFET connects the backup battery to
VOUT.
VOUT – VBATT
R
0.1µF
R
www.BDTIC.com/ADI
VOUT
VCC
RECHARGEABLE
BATTERY
VBATT
0.1µF
ADM69_A
ADM800_
Reset Output
Figure 22. Rechargeable Battery
Adding Hysteresis to the Power Fail Comparator
For increased noise immunity, hysteresis may be added to the
power fail comparator. Since the comparator circuit is noninverting,
hysteresis can be added simply by connecting a resistor between
the PFO output and the PFI input as shown in Figure 23. When
PFO is low, resistor R3 sinks current from the summing junction
at the PFI pin. When PFO is high, R3 sources current into the
PFI summing junction. This results in differing trip levels for the
comparator. Resistors R1 and R2 therefore set the trip point
while R3 adds hysteresis. R3 should be larger than 10 kΩ so that
it does not cause excessive loading on the PFO output. Additional noise rejection and filtering may be achieved by adding a
capacitor from PFI to GND.
The internal voltage detector monitors VCC and generates a
RESET output to hold the microprocessor’s RESET line low
when VCC is below the reset threshold. An internal timer holds
RESET low for 200 ms after VCC rises above the threshold.
This prevents repeated toggling of RESET even if the 5 V
power drops out and recovers with each power line cycle.
Early Power Fail Detector
The input power line is monitored via a resistive potential divider connected to the Power Fail Input (PFI). When the voltage at PFI falls below 1.25 V, the Power Fail Output (PFO)
drives the processor’s NMI input low. If a Power Fail threshold
of 7 V is set with resistors R1 and R2, the microprocessor will
have the time when VCC drops below 7 V to save data into
RAM. Power supply capacitance will extend the time available.
This will allow more time for microprocessor housekeeping
tasks to be completed before power is lost.
–10–
REV. 0
ADM691A/ADM693A/ADM800L/M
RAM Write Protection
The CEOUT line drives the Chip Select inputs of the CMOS
RAM. CEOUT follows CEIN as long as VCC is above the reset
threshold. If VCC falls below the reset threshold, CEOUT goes
high, independent of the logic level at CEIN. This prevents the
microprocessor from writing erroneous data into RAM during
power-up, power-down, brownouts and momentary power interruptions. The LOW LINE output goes low when VCC falls
below the reset threshold.
RESET also goes low if the Watchdog Timer is enabled and
WDI remains either high or low for longer than the watchdog
timeout period.
The RESET output has an internal 1.6 mA pullup, and can either connect to an open collector RESET bus or directly drive a
CMOS gate without an external pullup resistor.
INPUT POWER
+5V
0.1µF
Watchdog Timer
The microprocessor drives the WATCHDOG INPUT (WDI)
with an I/O line. When OSC IN and OSC SEL are unconnected, the microprocessor must toggle the WDI pin once every
1.6 seconds to verify proper software execution. If a hardware or
software failure occurs such that WDI not toggled a 200 ms
RESET pulse will be generated after 1.6 seconds. This typically restarts the microprocessor’s power-up routine. A new
RESET pulse is issued every 1.6 seconds until WDI is again
strobed.
0.1µF
VCC
3V
BATTERY
VBATT
BATT VOUT
ON
CEOUT
ADM691A
ADM693A CEIN
ADM800L
PFI ADM800M
R1
ADDRESS
DECODE
A0–A15
GND
R2
WDI
NC
OSC IN
OSC SEL
LOW LINE
The WATCHDOG OUTPUT (WDO) goes low if the watchdog timer is not serviced within its timeout period. Once WDO
goes low it remains low until a transition occurs at WDI. The
watchdog timer feature can be disabled by leaving WDI unconnected. OSC IN and OSC SEL also allow other watchdog timing options.
I/O LINE
PFO
NMI
RESET
WDO
RESET
RESET
0.1µF
SYSTEM STATUS
INDICATORS
Figure 24. Typical Application Circuit
www.BDTIC.com/ADI
REV. 0
CMOS
RAM
–11–
µP
ADM691A/ADM693A/ADM800L/M
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
16-Lead TSSOP
(RU-16)
16-Lead Plastic DIP
(N-16)
1
8
PIN 1
16
0.280 (7.11)
0.240 (6.10)
0.060 (1.52)
0.015 (0.38)
0.210 (5.33)
MAX
0.325 (8.25)
0.300 (7.62) 0.195 (4.95)
0.115 (2.93)
1
0.130
(3.30)
MIN
0.160 (4.06)
0.115 (2.93)
0.022 (0.558)
0.014 (0.356)
0.100
(2.54)
BSC
9
0.256 (6.50)
0.246 (6.25)
9
0.177 (4.50)
0.169 (4.30)
16
8
PIN 1
0.015 (0.381)
0.008 (0.204)
0.070 (1.77) SEATING
0.045 (1.15) PLANE
0.006 (0.15)
0.002 (0.05)
SEATING
PLANE
0.0433
(1.10)
MAX
0.0118 (0.30)
0.0075 (0.19)
0.0256
(0.65)
BSC
16-Lead Wide SOIC
(R-16W)
0.0500
(1.27)
BSC
0.1574 (4.00)
0.1497 (5.80)
16
9
0.2550 (6.20)
0.2284 (5.80)
www.BDTIC.com/ADI
0.1043 (2.65)
0.0926 (2.35)
0.0192 (0.49)
SEATING 0.0125 (0.32)
0.0138 (0.35) PLANE
0.0091 (0.23)
1
8
PIN 1
0.0098 (0.25)
0.0040 (0.10)
0.0291 (0.74)
x 45°
0.0098 (0.25)
8°
0°
SEATING
PLANE
0.0500 (1.27)
0.0157 (0.40)
0.0500
(1.27)
BSC
0.0688 (1.75)
0.0532 (1.35)
0.0192 (0.49)
0.0138 (0.35)
0.0099 (0.25)
0.0075 (0.19)
0.0196 (0.50)
x 45°
0.0099 (0.25)
8°
0°
0.0500 (1.27)
0.0160 (0.41)
PRINTED IN U.S.A.
PIN 1
0.4193 (10.65)
0.3937 (10.00)
9
8
0.0118 (0.30)
0.0040 (0.10)
0.028 (0.70)
0.020 (0.50)
8°
0°
0.3937 (10.00)
0.3859 (9.80)
0.2992 (7.60)
0.2914 (7.40)
1
0.0079 (0.20)
0.0035 (0.090)
16-Lead Narrow SOIC
(R-16N)
0.4133 (10.50)
0.3977 (10.00)
16
C2198–12–10/96
0.201 (5.10)
0.193 (4.90)
0.840 (21.33)
0.745 (18.93)
–12–
REV. 0